Polymeric films are useful in a wide variety of applications, particularly for use in packaging products. Besides exhibiting the ability to be processed on high speed equipment such as form/fill/seal machines, an important consideration in designing certain packaging films is the ability to provide barrier properties. In particular, water and oxygen barrier properties are often important considerations for packaging films.
There are two general types of form/fill/seal methods. In a horizontal form/fill/seal apparatus, individual pouches or packages are formed by folding the multi-layer film and providing horizontal and/or vertical seals along the length of the folded web, depending upon whether the packaging is along a horizontal packaging line such as for box overwrap, or along a pouch line for forming a pouch. The individual packages may typically be separated at a seal area. Optionally, the bottoms of the pouches or packages can also be sealed. After the pouch or package is formed and filled, the top of the pouch or package is sealed. Similarly, in vertical form/fill/seal apparatus, the continuous web is formed around a tube and the web is immediately joined together by a longitudinal vertically oriented sealing jaw as either a lap seal or a fin seal and transversely along the top and bottom margins of the bag or package. For purposes herein, the term package or packaging may be defined broadly to encompass horizontal formed overwrap packages, pouches, vertically formed packages, and bags. For additional information regarding such packaging systems, see U.S. Pat. No. 4,671,047 to Mugnai; U.S. Pat. No. 4,807,420 to Barker; U.S. Pat. No. 4,090,344 to Kelly; and U.S. Pat. No. 4,937,112 to Schirmer.
It is known to provide metallic layers or coatings on the surface of polymeric films to provide barrier properties. The metallic layers may be used on polymeric films used in form/fill/seal applications as well as a vide variety of other polymeric film applications such as pouches and bags. A metallic layer or coating is typically applied by vapor deposition methods. U.S. Pat. No. 5,487,940 to Bianchini et al. and U.S. Pat. No. 6,420,041 to Amon et al. describe and refer to numerous exemplary metallized films. Metal layers are well known in the packaging industry and can be deposited using any known method, for instance, vacuum deposition, electroplating, sputtering, etc. In many applications, the metal layer is one of vacuum deposited aluminum, copper, silver, chromium, gold, and mixtures thereof, with vacuum deposited aluminum being the most commonly used. Metallized films are widely used for their moisture barrier properties.
Various coatings are also applied to the surface of polymeric films to enhance barrier properties. Acrylic-containing coatings that offer barrier properties are known. An acrylic coating may be applied to one side of a film substrate and another heat sealable coating, such as polyvinylidene chloride (PVdC), or another acrylic coating, is coated on the other side of the film substrate. Acrylic-containing coating formulations provide films with a good coefficient of friction which contributes to good machinability characteristics. Acrylic-based coatings also provide films with good barrier characteristics which improve flavor and aroma protection. Such coatings are described in U.S. Pat. No. 4,058,649 to Steiner and U.S. Pat. No. 4,058,645 to Steiner. The PVdC coating or other type of acrylic coating is usually on the inside (e.g., the product side) of the film and provides high seal strength, good hot tack characteristics and barrier properties. These heat sealable coatings have glass transition (“Tg”) temperatures which are higher than room temperature. Such a coated film is disclosed in U.S. Pat. No. 4,403,464 to Duncan.
Polymeric films may also be provided with coatings incorporating polymers such as ethylene vinyl alcohol (“EVOH”) co-polymers and polyvinyl alcohol (“PVOH”) co-polymers. U.S. Pat. No. 6,472,470 to Fujiwara, et al. discloses EVOH copolymers that are described as having excellent thermal stability, water resistance, and gas-barrier properties. The EVOH copolymers are prepared as aqueous coating solutions. The aqueous solutions are described as having good stability when allowed to stand for a long time at low temperatures. U.S. Pat. No. 5,827,615 to Touhsaent et al. discloses the use of EVOH copolymer layers in film structures.
U.S. Pat. No. 5,547,764 to Blais, et al. discloses the use of solutions incorporating at least two PVOH co-polymers having differing degrees of hydrolysis. The solutions are used to provide coatings for producing films exhibiting low oxygen transmission characteristics. The solutions may include a cross-linking agent. Oxygen transmission rates at 0% relative humidity and 75% relative humidity are disclosed. Solutions of the PVOH co-polymers are described as exhibiting improved pot life and shelf life. In certain Examples, a PVOH solution with a pot life of about 72 hours is disclosed. Other cross-linked PVOH solutions and coatings are disclosed in U.S. Pat. No. 5,512,338 to Bianchini et al. and U.S. Pat. No. 5,604,042 to Bianchini et al. Additional PVOH co-polymer solutions and coatings are disclosed in U.S. Pat. No. 5,508,113 to Knoerzer; U.S Pat. No. 5,525,421 to Knoerzer; U.S Pat. No. 5,547,764 to Blais et al.; U.S. Pat. No. 5,552,212 to Knoerzer; U.S Pat. No. 5,731,093 to Chang et al.; and U.S. Pat. No. 6,444,750 to Touhsaent.
Coating solutions and coatings incorporating a vinyl alcohol/amine copolymer are disclosed in U.S. Pat. No. 5,776,618 to Lu.